1. Field of the Invention
The present invention relates to methods of manufacturing products comprising acrylic materials. In particular, this invention relates to methods for polishing soft acrylic articles to remove rough surfaces and tool or machining marks.
2. Description of Related Art
Soft acrylic materials are used in the manufacture of a wide variety of products. Because soft acrylic materials are generally compatible with biological tissues and fluids, they can be particularly useful in making products for biomedical applications. Examples of such soft acrylic products include soft contact lenses and soft prosthetic implants, such as intracorneal and intraocular lenses, corneal inlays used during refractive surgery, and intracapsular rings used to support the natural lens capsule during ophthalmic surgery.
A highly polished finish, free of sharp edges or surface irregularities, is required in many biomedical applications. Implantable products, such as intraocular lenses, are in direct contact with body tissues and the tearing or abrading of tissue by rough surfaces could result in rupture of blood vessels, irritation or other trauma to the tissue. Even minute irregularities can cause irritation of body tissues. This is a particularly serious problem with contact lenses and portions of intraocular lenses that contact the eye, where the tissue is extremely sensitive.
The use of soft acrylic materials for intraocular lenses is a relatively new development. Intraocular lenses formed of soft acrylic material are advantageous in that they can be folded and inserted through smaller incisions in the cornea than previously possible, resulting in fewer post-operative complications. Rough edges resulting from the cutting of lens blanks or flashing generated during molding can cause intraocular irritation.
In addition, soft contact lenses require a highly polished finish to prevent irritation of the interior of the eyelid and corneal epithelium. The eye is extremely sensitive to imperfections in contact lenses, and even slight ridges resulting from the molding process can produce irritation and discomfort. Expensive molding procedures or individual hand-grinding techniques may be used to provide the desired finish for these lenses.
Mechanical devices utilizing smooth, frictionless movement also require highly polished, smooth surfaces of their soft acrylic products. Obtaining such a highly polished, smoothly-finished soft acrylic article is often difficult as these products are manufactured by curing acrylic material in molds, wherein even the most precise dies result in some flashing and/or irregular edges. The products may be trimmed and polished, but these finishing procedures are generally done by hand, and are both time consuming and expensive, as well as imprecise, so that they do not result in the totally smooth or regular surface required. Further, many of these articles, particularly those for biomedical applications, are relatively small, and/or irregularly shaped, causing difficulties in obtaining the desired finish, and/or clarity.
For silicone materials, such as silicone rubbers and silicone elastomers, tumble polishing processes are known. See, for example, U.S. Pat. No. 5,133,159. However, the tumble polishing methods known for articles made from silicone materials are not adequately applicable to articles made from soft acrylic materials. The removal of imperfections from small and irregularly shaped soft acrylic products is an unsolved problem in the art. It would be of great utility to provide a simple, economic, and effective method for polishing and/or clarifying soft acrylic articles for industrial, medical, and mechanical purposes.
Commonly assigned, copending U.S. patent application Ser. No. 08/962,604 discloses methods for tumble polishing soft acrylic articles. The methods comprise a cryogenic polishing step and a cleaning step.